1. Field of the Invention
This invention relates to a sewing machine, more particularly to a thread cutting device for a sewing machine.
2. Description of the Related Art
In U.S. Pat. No. 5,887,535, there is disclosed a thread cutting device for a sewing machine that includes a base plate, a feed plate, a cutting plate, a driving rod, a driving unit, a crank, a torsion spring, and a reed spring. Although the thread cutting device can cut effectively a row of threads, it has a relatively complicated structure. As a result, it is difficult to adjust the positions of some movable elements of the thread cutting device relative to the threads to be cut. Furthermore, each of the feed plate and the cutting plate has a path of travel which is relatively long, thereby resulting in a relatively large amount of noise during operation thereof.
The object of this invention is to provide a thread cutting device for a sewing machine which has advantages of simple structure, convenient position adjustment, short paths of travel of movable elements, and reduced amount of noise.
According to this invention, a thread cutting device for a sewing machine includes a front pivot member and a rear pivot member which extend through an elongated cutting plate and an elongated swing plate that is disposed between the cutting plate and a base plate. A driving rod is mounted swingably on the base plate, and has an end that is received slidably within a transverse slide slot in the cutting plate. When the driving rod is swung by a driving unit, the cutting plate and the swing plate rotate to align a cutter of the cutting plate with a needle. Then, the cutting plate is guided to move toward the needle relative to the swing plate. Accordingly, the paths of travel of the cutting plate and the swing plate are relatively short, thereby reducing noise resulting from the operation thereof. Each of the front and rear pivot members includes an eccentric wheel element that is formed with a threaded hole and that is rotatable relative to the cutting plate and the swing plate, and a bolt that extends threadably through the threaded hole in the eccentric wheel element to engage a threaded hole in the base plate. In a case where the cutter cannot be brought into alignment with the threads to be cut, as long as the eccentric wheel elements are rotated on the base plate, the cutter can come into alignment with the threads. Thus, the position adjustment of the cutting plate and the swing plate can be performed easily.